struct Node
{
	Node(int v) :m_next(NULL), m_value(v) {}
	int m_value;//值
	Node* m_next;//指向下一个节点的指针
};
Node* IsCircle(Node* head)
{
	//找相同的地址，有则有环，反之无环，数据有可能一样，但是地址肯定不一样
	set<Node*> ss;//新的容器
	Node* p = head;
	while (p != NULL)
	{
		if (ss.find(p) != ss.end())
		{
			return p;
		}
		ss.insert(p);
		p = p->m_next;
	}
	return p;
}
void main()
{
	Node* head = NULL;
	Node a(1), b(2), c(3), d(4), e(5);
	head = &a;//头节点指向第一个有数值的节点的地址
	a. m_next = &b;//创建链表
	b.m_next = &c;
	c.m_next = &d;
	d.m_next = &e;
	e.m_next = &c;
	Node* p = IsCircle(head);
	if (p != NULL)
	{
		cout << "有环" << endl;
		cout << p->m_value << endl;
	}
	else
		cout << "无环" << endl;
}